We are interested in how the three cone classes of the cone mosaic are arranged, how genetics steers this organization, and how signals from the cones are processed to ultimately provide our perception of color. Recently, adaptive optics has been used to obtain high-resolution images of the cone mosaic in vivo. The purpose of this proposal is to exploit this new technique to address the above questions. In order to investigate the arrangement of the three cone classes, we will examine the cone mosaic at a number of different retinal locations for a number of color normal males. To date, this technique has only been used on a small number of subjects, though with recent improvements, the method is becoming more and more practical. The ratio of L to M cones in female carriers of color vision defects will be examined to help assess the role of X-inactivation in forming the cone mosaic. Finally, in an effort to understand how the signals from the different cone types are utilized, we will stimulate single photoreceptors in the living human eye using adaptive optics and determine the visual sensations that arise from quantum catches in single cone photoreceptors. This will be done in subjects for whom we also have a representation of their cone mosaic, to be able to selectively stimulate cones from a particular class.